As an apparatus for polishing a surface of a workpiece such as a silicon wafer, there are a single-side polishing apparatus, in which the workpiece is polished by each side, and a double-side polishing apparatus, in which the both sides of the workpiece are polished at the same time.
For example as shown in FIG. 10, a common single-side polishing apparatus comprises a turn table 88 onto which a polishing pad 89 is attached, a polishing agent supply mechanism 90, a polishing head 81 and the like. This polishing apparatus 82 polishes a workpiece W by holding the workpiece W with the polishing head 81, supplying a polishing agent onto the polishing pad 89 through the polishing agent supply mechanism 90, rotating the turn table 88 and the polishing head 81 respectively, and bringing a surface of the workpiece W into sliding contact with the polishing pad 89.
As a method for holding the workpiece with the polishing head, for example, there is a method of attaching the workpiece onto a flat disk-shaped plate through an adhesive such as a wax. Other than that, particularly as a holding method of suppressing rise and sag on an outer circumferential portion of the workpiece and of improving flatness of the whole workpiece, there is a so-called rubber-chuck method in which a workpiece holding portion is made of an elastic film, a pressurized fluid such as air is poured into a back face of the elastic film, and the elastic film is inflated by a uniform pressure so as to press the workpiece toward the polishing pad (See Patent Literature 1, for example).
An example of the structure of a conventional polishing head by the rubber-chuck method is schematically shown in FIG. 9. An essential part of this polishing head 101 consists of an annular rigid ring 104 made of SUS and the like, the rubber film 103 bonded to the rigid ring 104, and a mid plate 105 joined to the rigid ring 104. A sealed space 106 is defined by the rigid ring 104, the rubber film 103, and the mid plate 105. An annular template 114 is provided concentrically with the rigid ring 104 in a peripheral portion on a lower face portion of the rubber film 103. The pressure of the space is adjusted, for example, by supplying a pressurized fluid with a pressure adjustment mechanism 107 in a center of the mid plate 105. A pressing means, not shown, for pressing the mid plate 105 in the direction of the polishing pad 109 is provided.
With the polishing head 101 configured as above, the workpiece W is held on the lower face portion of the rubber film 103 through a backing pad 113, an edge portion of the workpiece W is held with the template 114, and the workpiece W is polished by bringing it into sliding contact with the polishing pad 109 attached onto an upper face of the turn table 108 by pressing the mid plate 105.
With regard to polishing of the workpiece by using the above-described polishing head, for the purpose of Improving uniformity of the polishing, there are disclosed a carrier head by the rubber-chuck method that enables a wafer to be pressed with a plurality of annular portions concentric with one another (See Patent Literature 2) and a substrate-holding apparatus in which a plurality of pressure chambers are provided inside a space formed between an elastic pad and a holding member (See Patent Literature 3).